612 
ME.  J.  LISTEE  ON  THE  PAETS  OF  THE  NEETOUS  STSTE3I 
Abundantly  sufficient  proof  had  now  been  obtained  that  the  cerebro-spinal  axis  does 
contain  a nervous  centre  for  regulating  the  contractions  of  the  arteries  of  the  feet. 
But  it  was  uncertain  whether  that  centre  were  confined  to  any  one  part  of  the  cord,  or 
diffused  extensively  through  it  and  the  brain ; or  even  whether  a similar  office  might  not 
also  be  discharged  by  some  of  the  sympathetic  ganglia.  With  a ’^iew  to  determining 
these  points,  which  are  of  great  physiological  interest,  several  experiments  were  per- 
formed, some  of  which  it  will  be  necessary  to  relate ; but  in  order  to  make  their  descrip- 
tion intelligible,  it  wiU  be  well  to  say  a few  words  regarding  the  arrangement  of  the 
spinal  cord  in  the  frog.  It  does  not  occupy  the  entire  length  of  the  spinal  canal,  but 
extends  backwards  only  seven-tenths  of  the  distance  from  the  occiput  to  the  sacrum, 
while  the  posterior  three-tenths  of  the  canal  contain  merely  the  cauda  equina,  including 
a slender  fihform  prolongation  of  the  cord,  which,  though  apparently  composed  in  part 
of  nervous  matter,  seems  to  give  off  no  nerves. 
In  the  accompanying  sketch  of  the  superior  aspect  of  the  brain  and 
cord  of  a frog,  magnified  two  diameters,  the  distance  fi’om  aXoh  repre- 
sents the  length  of  the  spinal  canal.  The  principal  nerves  for  the  hind 
legs  spring  from  the  cord  near  its  extremity,  but  other  smaller  branches 
with  the  same  destination  arise  nearly  as  far  forward  as  the  middle 
of  its  length.  There  are  also  connecting  filaments  between  these  and 
some  nerves  for  the  abdominal  parietes,  taking  origin  slightly  further 
forward  than  the  middle  of  the  cord.  Thus  the  nerves  for  the  poste- 
rior extremities  are  furnished  chiefly,  but  not  quite  exclusively,  from 
the  posterior  half  of  the  cord.  To  expose  the  cord  in  its  entire  length 
without  injury  to  it  or  any  of  its  slender  branches  is  troublesome, 
and  also  involves  much  loss  of  blood.  It  is  therefore  very  desmable  to 
be  able  to  come  at  once  on  any  part  of  the  cord  you  may  desire, 
without  laying  open  the  whole  canal.  This  can  be  readily  done  from 
the  data  above  given.  The  articulation  between  the  occiput  and  first 
felt  through  the  skin,  as  also  can  the  commencement  of  the  sacrum ; and  the  distance 
between  these  points  is  the  length  of  the  spinal  canal.  This,  multiplied  by  O’Y.  is  the 
length  of  the  cord : the  requisite  fraction  of  this  length  is  then  measured  from  the 
occiput  and  gives  the  place  required. 
Assistance  may  also  be  derived  from  the  circumstance  that  the  posterior  edges  of  the 
scapulae  correspond  very  nearly  with  the  mid-length  of  the  cord,  overlapping  the  posterior 
half  by  only  about  -^(jth  of  the  whole. 
To  proceed  with  the  experiments.  On  the  16th  of  April,  a large  frog  being  put 
under  chloroform,  the  entire  brain  was  removed  about  3 o’clock  p.m.  mthout  injui-y  to 
the  cord.  After  this  operation,  the  arteries,  which  had  previously  been  of  pretty  full  size 
elucidating  the  nature  of  inflammation.  Little  if  any  reflex  action  of  the  limb  occurs  when  irritants  are 
applied  to  the  web  ; and  if  no  great  amount  of  blood  have  been  lost  in  the  operation,  the  creature  will  survive 
it  a long  while,  e.  g.  eight  days  in  one  case. 
vertebra  can  be 
